Inspection raises concerns about structural integrity
By Ann McCreary
The levee that runs along the perimeter of the Twisp Park is overgrown with trees and shrubs, and the U.S. Army Corps of Engineers wants the vegetation removed.
Constructed more than 50 years ago to prevent the Twisp River from flooding the park and surrounding area, the 720-foot-long levee is thick with a variety of bushes and trees that nearly obscure the view of the river.
During a recent, routine inspection of the levee, the Corps of Engineers, which is responsible for certifying the safety of dikes and levees, said Twisp’s dike could lose certification if the foliage isn’t removed.
“It undermines the integrity of the levee,” said Twisp Public Works Director Andrew Denham.
The Corps of Engineers inspects the levee every two years, and advised the town during the previous inspection to remove the trees, said Denham, who was not public works director at the time.
Denham plans to hire a contractor to clear most of the offending trees and shrubs next month, after leaves have fallen off.
Complying with the Corps of Engineers is important in order to maintain certification of the levee, Denham said. If the levee is rated “unacceptable” by the Corps, it means the town won’t get assistance from the Corps if floodwaters threatened the levee or the structure was breached.
“Last winter when we had the ice dam, I called and they had a team of their engineers over here. That’s a big deal at no cost,” said Denham, referring to an ice buildup along the levee last January.
The Corps rates levees as acceptable, minimally acceptable or unacceptable. The levee by the Twisp Park has been given a minimally acceptable rating in 2011, 2014 and 2016.
The excess growth of trees and shrubs is considered a deficiency that threatens “the integrity, operation, and inspection of the levee and could prevent the levee system from functioning as intended,” according to the 2014 report from the Corps.
Inspectors from the Corps said they want all trees on the levee and within 15 feet of the base — or “toe” — of the levee to be removed. That would include several large old pine trees in the Town Park that are near the base of the levee.
Denham said he plans to leave the pines in the park, and on the levee itself, in place. He said he’ll direct the contractor to take out small and medium trees — mostly elms and cottonwoods — that will grow into big trees.
He also wants to leave in place shrubs with berries that provide food for wildlife.
If the town removes most of the trees and shrubs, Denham said he expects the Corps will provide the needed certification.
“If we make an effort to protect the levee, we’ll be in compliance enough to get an acceptable rating” from the Corps of Engineers,” he said.